1. Field of the Invention
This invention relates to processes for producing granular composite fertilizer compositions and to the products produced by such processes. More particularly, it relates to processes for producing granular composite fertilizer compositions including nitrogen sources in combination with phosphorus sources and/or potassium sources and/or secondary nutrient sources and/or micronutrient sources and/or mixtures thereof employing a single reaction/granulation step to produce the granular composite fertilizer compositions from liquid mixtures of urea and formaldehyde. The invention further relates to the granular compositions prepared by such processes.
2. Description of Related Art
Urea formaldehyde condensation products containing methylene urea polymers of varying chain length have been widely used heretofore as controlled or slow release nitrogen fertilizers. Additionally, a variety of processes for producing controlled or slow release fertilizer compositions are known and, particularly, processes for producing controlled or slow release reaction products of urea and formaldehyde for fertilizer applications. Traditionally, controlled or slow release urea-formaldehyde reaction products for fertilizer applications have been prepared in order to achieve the proper degree of polymerization required to provide the desired fertilizer characteristics.
Normally, these products have been prepared by first reacting urea and formaldehyde at elevated temperatures in an alkaline solution to produce methylol ureas. The reaction mixtures have then been acidified causing the methylol ureas to polymerize to form methylene urea polymers of varying chain length. Then, in order to produce NPK composite granular fertilizers, further processing steps usually have been required after the reaction step such as formulating additional ingredients with the reacted components and/or granulating the resulting products in a separate granulation step to produce composite granular end products.
For example, U.S. Pat. No. 4,089,899 discloses what is there described as a controlled reaction system for preparing slow release ureaform compounds with a low average degree of polymerization. The process disclosed therein involves the reaction of urea and formaldehyde in the presence of an acid catalyst for extended reaction times at low temperatures in order to produce nitrogen only fertilizer compositions having nitrogen content greater than 41% (by weight). For the processes of this patent to produce composite compositions, time consuming and expensive multiple step processing of the raw materials would be required which would be commercially disadvantangeous.
U.S. Pat. No. 3,198,761 discloses processes for producing products by reacting a urea-formaldehyde resin into a solid sheet which is milled and screened to provide a granular product having a desired particle size. These processes are known as the "Nitroform" processes and as described in this patent relate only to the preparation of nitrogen fertilizers and are not directed to the production of composite compositions. Furthermore, as discussed above relative to U.S. Pat. No. 4,089,899, for the processes of this patent to produce composite compositions, the implementation of time consuming and expensive multiple stage processing of the raw materials would be required, rendering the process commercially disadvantangeous.
Other known processes for producing granular controlled or slow release fertilizer products are disclosed, for example, in U.S. Pat. Nos. 3,076,700; 3,705,794 and 3,989,470. Essentially, the products described therein are produced by reacting ureaformaldehyde resins into rigid foams which are dried, milled and screened to the desired granular size. As opposed to the technology disclosed in U.S. Pat. No. 3,198,761 which is suitable solely for production of nitrogen only products, the processes disclosed in these patents have the flexibility of producing composite fertilizers by slurrying other finely ground additives such as phosphorus and/or potassium salts into the resin prior to the foaming reaction.
Thus, the processes disclosed in U.S. Pat. Nos. 3,076,700; 3,705,794 and 3,989,470 represent an advancement in respect to their ability to produce a wide variety of N-P-K minor element ratios in the products and are not restricted to the production of nitrogen only products. However, these processes are restricted in the range of N-P-K ratios in view of the limit on the amount of solids which can be slurried into the ureaformaldehyde resin without adversely impacting the condensation reaction. Furthermore, the products produced in accordance with the disclosures of U.S. Pat. Nos. 3,076,700; 3,705,974 and 3,989,470 have been found to be quite friable or fragile and susceptible to being dusty as a result of handling, bagging and the like. Also,these products have a very broad particle size distribution resulting in a low Uniformity Index (low UI).
U.S. Pat. No. 3,677,736 discloses a multi-stage process for producing a liquid fertilizer suspension of ureaform. Broadly, the process involves the reaction of urea and formaldehyde in the presence of ammonia at an alkaline pH followed by acidification. The final product is stated to be a liquid fertilizer rather than a granular composite fertilizer composition.
U.S. Pat. No. 4,025,329 discloses another process for producing carrierless products. In this process a granular product is formed, for example, in accordance with the disclosures in U.S. Pat. Nos. 3,705,794 and 3,989,470 and then the granules are compacted with other nutrient or pesticide additives to produce a product of uniform composition and particle size. The density of the granules produced is greater than 1.4 and the granular size is greater then 30 mesh, with substantially all of the granules having a ratio of largest to smallest granule of less than 3:1. Again, the production of composite fertilizers employing the techniques described in this patent require economically disadvantageous two step processes and the products produced would be angular in nature resulting in abrasion to fines particles and dust generation during handling. For example, the products present a dust plume problem when poured from their storage container. This dust plume results from abrasion of the angular edges of the product particles during handling and from surface adhesion of dust to the product during the manufacturing process. Additionally, these high density products have been found to present a dispersibility problem in regard to their use on turf. In this regard, the particles size of these products is too large and the products do not disperse adequately to penetrate the turf canopy after application. Thus, the product remains on the surface to be picked up on shoes, golf balls and the like as they travel over the turf
A further experimental multi-stage process for producing ureaform fertilizer products is disclosed in an article entitled "Reactions of Molten Urea with Formaldehyde", by Thomas P. Murray et. al., published in Ind. Eng. Chem. Prod. Res. Dev., 1985, at 420-425. The process disclosed therein entails the reaction of molten urea with paraformaldehyde either by mixing paraformaldehyde into melted urea at temperatures of between 130 degrees and 140 degrees C. or by premixing the paraformaldehyde with the urea and heating the solid mixture to 130 degrees C. with stirring. Thereafter, the molten reaction mixture resulting from either of the procedures is cooled to form a solid sheet and the sheet is ground in a second step to form granular fertilizer products.
U.S. Pat. Nos. 4,378,238 and 4,411,683 disclose processes for producing slow release granular products having at least 60% of the polymeric nitrogen in the form of methylene diurea (MDU) and dimethylene triurea (DMTU). The processes disclosed therein for producing fertilizer products includes the step of reacting aqueous mixtures of urea, formaldehyde and ammonia at elevated temperatures to produce methylol ureas. Then, phosphorus and/or potassium sources are slurried into the aqueous mixture and acid is added directly to the reaction mixture. The acidified mixture is reacted to form a foamed condensation reaction products which are dried and milled into final products. In regard to the process disclosed in U.S. Pat. Nos. 4,378,238 and 4,411,683, it has been found that the process therein cannot be economically or feasibly conducted to produce commercially acceptable products which do not employ an absorbent carrier capable of absorbing liquids to provide a granular structure to the final product. Typical examples of commonly used carriers which are not required for use in forming products of the present invention are vermiculite, perlite and corncobs. Furthermore, as described hereinafter, the process of the present invention does not employ ammonia in a liquid reaction mixture as was described in the processes disclosed in U.S. Pat. Nos. 4,378,238 and 4,411,683 since it was found that the inclusion of ammonia in the aqueous reaction mixture contributed to the above described problems with these prior art processes. Still further, it should be noted that the process of the present invention, as described herein, does not require the use of absorbent carrier materials to provide granular structures.
U.S. Pat. No. 5,102,440 discloses a process which comprises preparing a mixture of urea and formaldehyde, heating the reaction mixture until essentially all of the formaldehyde in the mixture is fully reacted and a molten or liquid urea-formaldehyde resin is formed. Then, the molten fully reacted,urea-formaldehyde resin is sprayed on small finely divided solid raw material particles and the urea-formaldehyde resin acts as a binder to agglomerate the solid particles within a matrix formed by the urea-formaldehyde resin in order to produce a granular product of a desired size. The resulting product is allowed to cool and solidify into a hard granular carrierless product which exhibits slow release nitrogen properties. The products prepared in accordance with the teachings of this patent have been found to exhibit highly desirable functional characteristics. However, as a result of the two step process disclosed in that patent, products cannot be produced having nitrogen distribution levels characterized by low urea content and significantly higher polymeric nitrogen content as is produced by the process of the present invention which enables production of products including 40% or less urea content (preferably, less than 30% and, most preferably, less than 20%) and at least 50% polymeric nitrogen content (preferably, greater than 60% and, most preferably, greater than 80%).
Furthermore, the processes disclosed in U.S. Pat. No. 5,102,440 do not offer as much flexibility in producing variable size granules, particularly with regard to smaller particle sizes and do not offer the uniformity of particle size (UI) as do the products produced by the processes of the present invention.
Accordingly, none of the prior processes are suitable for producing controlled or slow release fertilizer compositions having the desired characteristics either because of process or product shortcomings such as the cost effectiveness of the process, the ability to include additive products in the urea-formaldehyde reaction product and the physical properties of the product produced by those prior art processes.